Nowadays there is a big hype about IoT devices and it’s not surprising. Many creative project and business idea is based on this new technology, the opportunity is limitless. I also had a good project idea – to design a battery operated motion sensor device.

First I started to think on system level, and later on I have realized that as always, the power supply circuit is one of the most critical part of the design. A battery operated IoT device has to have low power consumption and because of this reason, a DC-DC converter is almost always the best choice. I defined a few criteria and after that I started to search for the most suitable DC-DC converter chip for my project.

- It is a Buck-Boost converter with 1 A switches and with an input voltage range from 2.5 V to 5.5 V. This means I can use different battery types for generating the required 3.3 V system rail. It operates in Buck mode if I use a 3.6V Lithium thionyl chloride battery or it will operate in Boost mode in the case of two alkaline battery in series. This gives me a huge flexibility and the coolest thing is that it provides a seamless transition from Buck to Boost or from Boost to Buck operation.

- The device has an efficiency > 90% in Boost Mode and > 95% in Buck Mode. No question, these are industry leading numbers. With the “Automatic Power Save Mode” feature and its low quiescent current (< 60 μA) I was able to further optimize the power consumption of my IoT device and extend the battery life.

- This converter IC is available in a 2.5mm x 2.5mm 12-pin HotRod™ QFN package which was good news for me, because my plan was to build a prototype with a single soldering iron without a hot air station. With a magnifier and a little patience it is possible to hand solder these QFN packages.

During the design phase I strictly followed the datasheet and the reference design provided by TI. The quality of the TI datasheets are amazing. I was able to find all the required information to finish the schematic and the PCB design. After assembling my first prototype it started to work for the first time. I was completely satisfied.

Here is my final schematic:

Of course every design can be fine-tuned. This requires the right tools and the right knowledge on power supply design topic. If I could win a Fundamentals of Power Supply Design book written by Robert A. Mammano, I could dive more deeply into this topic, and design more sophisticated power supplies for my next projects.